linux-kernel - Re: [PATCH] sh: dma: Add missing IS

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Message-ID: <CAMuHMdVGhd3KfRq9F+-Qzc7q5kJyczG1RRQDpgs4FqJpPwK4QA@mail.gmail.com>
Date:   Sat, 8 Jun 2019 14:26:08 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Rolf Evers-Fischer <embedded24@...rs-fischer.de>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Linux-sh list <linux-sh@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sh: dma: Add missing IS_ERR test

Hi Rolf,

Thanks for your patch!

On Fri, Jun 7, 2019 at 2:04 PM Rolf Evers-Fischer
<embedded24@...rs-fischer.de> wrote:
> get_dma_channel may return ERR_PTR, so a check is added.

It may also return NULL...

> --- a/arch/sh/drivers/dma/dma-api.c
> +++ b/arch/sh/drivers/dma/dma-api.c
> @@ -94,7 +94,7 @@ int get_dma_residue(unsigned int chan)
>         struct dma_info *info = get_dma_info(chan);
>         struct dma_channel *channel = get_dma_channel(chan);
>
> -       if (info->ops->get_residue)
> +       if (!IS_ERR(channel) && (info->ops->get_residue))
>                 return info->ops->get_residue(channel);

... in which case .get_residue() may crash, as some implementations
dereference the passed channel pointer.

Hence !IS_ERR_OR_NULL()?

I didn't check the other callers.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds